Several problems have been investigated related to photon migration in a turbid medium, with present and potential application to the laser used as a diagnostic tool. One such study explored the use of a telegrapher's equation as an approximation which incorporates effects of anisotropic scattering, i place of commonly-used diffusion approximations. Results provided by both a theoretical and a simulation study suggest that the telegrapher's equation, although suggested in the literature of tissue optics as a useful tool, provides an inadequate approximation. A random walk model has been developed for use in handling data in fluorescence spectroscopy measurement of various sorts. As part of a project on the application of the methods of statistical mechanics to the study of protein structure and folding, J.D. Bryngelson an G.H. Weiss have explored the replacement of rigid constraints in models of proteins with elastic constraints. These are not only more realistic from the point of view of physics but have proved to be easier to handle mathematically. Present work on this project is focused on incorporating models for flexibility in polymers into a study of the relation between the accuracy required in intermolecular potentials and the accuracy of structures predicted from NMR data. A collaborative project on overall reaction rates in systems with time-varying rate constants has been initiated by G.H. Weiss together with A. Szabo (NIDDK), A.M. Berezhkovskii (Karpov Institute of Physical Chemistry) and J. Spouge (NLM). This class of problems is suggested by the occurrence of fluctuating reaction states in many receptors. A first step in this investigation is to study very idealized physical models which embody time-gating. Thus far, solutions have been obtained for the simples case of two particles in which one changes its reactant state randomly in time. Other work on many-body effects on reaction rates is presently being pursued.